title: NIP6;1 is a boric acid channel for preferential transport of boron to growing shoot tissues in Arabidopsis.
abstract: Boron (B) in soil is taken up by roots through NIP5;1, a boric acid channel, and is loaded into the xylem by BOR1, a borate exporter. Here, the function of Arabidopsis thaliana NIP6;1, the most similar gene to NIP5;1, was studied. NIP6;1 facilitates the rapid permeation of boric acid across the membrane but is completely impermeable to water. NIP6;1 transcript accumulation is elevated in response to B deprivation in shoots but not in roots. NIP6;1 promoter-beta-glucuronidase is predominantly expressed in nodal regions of shoots, especially the phloem region of vascular tissues. Three independently identified T-DNA insertion lines for the NIP6;1 gene exhibited reduced expansion of young rosette leaves only under low-B conditions. B concentrations are reduced in young rosette leaves but not in the old leaves of these mutants. Taken together, these data strongly suggest that NIP6;1 is a boric acid channel required for proper distribution of boric acid, particularly among young developing shoot tissues. We propose that NIP6;1 is involved in xylem-phloem transfer of boric acid at the nodal regions and that the water-tight property of NIP6;1 is important for this function. It is proposed that during evolution, NIP5;1 and NIP6;1 were diversified in terms of both the specificity of their expression in plant tissues and their water permeation properties, while maintaining their ability to be induced under low B and their boric acid transport activities.
authors.affiliation: Graduate School of Agricultural and Life Science, University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Mayuki
authors.initials: M
authors.lastname: Tanaka
authors.forename: Ian S
authors.initials: IS
authors.lastname: Wallace
authors.forename: Junpei
authors.initials: J
authors.lastname: Takano
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Roberts
authors.forename: Toru
authors.initials: T
authors.lastname: Fujiwara
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D001692:Biological Transport; D001895:Boron / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005966:Glucuronidase / Q000032:analysis; D026901:Membrane Transport Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D016254:Mutagenesis, Insertional; D009865:Oocytes / Q000378:metabolism; D010539:Permeability; D052585:Phloem / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000032:analysis; D014867:Water / Q000378:metabolism; D014981:Xenopus; D052584:Xylem / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D026901:Membrane Transport Proteins; C535126:NIP6;1 protein, Arabidopsis; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D014867:Water; D005966:Glucuronidase; D001895:Boron